Criminal charges could be brought against traders implicated in the interest rate rigging scandal after the Serious Fraud Office announced on Friday that it had begun a formal investigation into attempts to fix Libor.

The director of the SFO David Green said he had "decided to formally accept the Libor matter for investigation" after reviewing the information provided by regulators which last week fined Barclays £290m for attempting to manipulate the price of the key interest rate known as Libor - the London interbank offered rate.

The investigation is understood to be into the wider market and not just Barclays.

The decision to embark on a formal investigation appears to been taken quickly as on Monday the SFO had said it was considering "whether it is both appropriate and possible to bring criminal prosecutions".

"The issues are complex and the assessment of the evidence the FSA has gathered will take a short time, but we hope to come to a conclusion within a month," the SFO had said on Monday.

The fine related to events that took place between 2005 and 2009 when the bank was found to have manipulated the prices it submitted to help its own traders and rival banks' traders. Part of the fine also related to attempts by the bank to lower its Libor submissions during the 2008 banking crisis to reduce the chance that it was regarded as being in financial difficulty - which it was not.

The decision by Green to take on the investigation comes at a difficult period for the SFO which has suffered a number of high profile setbacks, and as the Barclays chairman Marcus Agius prepares to appear before MPs on Tuesday.

The FSA has been providing information to the SFO and has already made it clear that Barclays is not the only bank under investigation for civil sanctions such as fines of the kind imposed on Barclays. On the day the Barclays fine was announced Tracey McDermott, acting director of enforcement and financial crime at the City regulator, said that a "number of other significant cross-border investigations in this area" were under way involving other banks. "The action against Barclays should leave firms in no doubt about the serious consequences of this type of failure," she said.

At this week's treasury select committee, Bob Diamond, the former boss of Barclays, had said: "I understand that there will be follow-up criminal investigations on certain individuals ... It's not up to us, but we are certainly not going to stand in the way of it".